Methods and nodes for facilitating a pdu session procedure in interworking networks

ABSTRACT

A method at a first node for facilitating a PDU session procedure for a UE in a first communication network, wherein the first communication network is interworking with a second communication network, and a second node supporting the interworking is selected for managing the PDU session, the method comprising: determining an indication which indicates whether the PDU session supports interworking with the second network; and sending the indication to the second node. According to various aspects and embodiments of the method, allocation of resources can be improved and the deployment can be simplified.

TECHNICAL FIELD

The non-limiting and example embodiments of the present disclosuregenerally relate to the technical field of communication network, andspecifically to methods and nodes for facilitating a Protocol Data Unit(PDU) session procedure for a User Equipment (UE) in a firstcommunication network, wherein the first communication network isinterworking with a second communication network.

BACKGROUND

This section introduces aspects that may facilitate a betterunderstanding of the disclosure. Accordingly, the statements of thissection are to be read in this light and are not to be understood asadmissions about what is in the prior art or what is not in the priorart.

Today, there are many kinds of communication networks to meet thedemands of communication of people and/or devices. In some cases, two ormore different networks will coexist with and interwork with each other,cooperating to provide a bigger coverage for the communication. Forexample, due to the gradual evolvement of the communication system, itcan be envisaged that in some cases, a next generation communicationnetwork, e.g., a 5th Generation System (5GS) network, will coexist withand interwork with a current generation communication network, e.g., anEvolved Packet System (EPS) network.

FIG. 1 illustrates the non-roaming architecture for interworking between5GS and EPC (Evolved Packet Core, the core network of an EPSnetwork)/E-UTRAN (Evolved UMTS Terrestrial Radio Access Network). In thefigure, the nodes PCF+PCRF (Policy Control Function+Policy and ChargingRule Function), PGW-C+SMF (Packet Data Network Gateway Control planefunction+Session Management Function) and UPF+PGW-U (User PlaneFunction+Packet Data Network Gateway User plane function) are supportinginterworking between 5GS and EPC, which are optional. UEs that are notsubject to 5GS and EPC interworking may be served by entities notsupporting interworking, i.e. either by PGW/PCRF or SMF/UPF/PCF. Also,in the roaming architecture (not illustrated) for interworking between5GS and EPC/E-UTRAN, the nodes PCF+PCRF, PGW-C+SMF and UPF+PGW-Usupporting the interworking may also exist.

Interworking between different networks makes it possible that the UEsin a network can connect to another network. However, it can also beenvisaged that due to some reasons, such as network capability and/ornetwork restriction of a UE, e.g., lack of related hardware and/orsoftware support, lack of money in the related account and so on, the UEin a first network may not connect to a second network which the firstnetwork is interworking with.

For example, in a 5GS network, the core network capability of a UE isindicated in a MM (Mobility Management) Core Network Capabilityinformation element (IE). The Core Network Capability informationelement (IE) may have e.g. two values, one value may be “N1 modesupported”, indicating a mode of the UE accessing the 5G core network issupported, the other value may be “S1 mode supported”, indicating a modeof the UE accessing the EPC core network is supported. In order toensure that the UE MM Core Network Capability information stored in theAMF (Access and Mobility Management Function) is up to date (e.g. tohandle the situation when the USIM (Universal Subscriber IdentityModule) is moved into a different device while out of coverage, and theold device did not send the Detach message; and the cases of inter-RATRegistration Area Update), the UE shall send the UE MM Core NetworkCapability information to the AMF during the Initial Registration andMobility Registration Update procedure within the NAS (Non-AccessStratum) message. The AMF shall store always the latest UE MM CoreNetwork Capability received from the UE. Any UE MM Core NetworkCapability that an AMF receives from an old AMF/MME is replaced when theUE provides the UE MM Core Network Capability with Registrationsignalling. If the UE's MM Core Network Capability information changes(in either CM-CONNECTED or in CM-IDLE state), the UE shall perform aRegistration Update (‘type’ different to ‘periodic’) when it nextreturns to NG-RAN (Next Generation Radio Access Network) coverage.

Also, a UE in a 5GS network will be subject to some mobilityrestrictions. Mobility Restrictions restrict mobility handling orservice access of a UE. The Mobility Restriction functionality isprovided by the UE (only for mobility restriction categories provided tothe UE), the radio access network and the core network. In CM-CONNECTEDstate, the core network provides mobility restrictions to the radioaccess network within Handover Restriction List (HRL). Mobilityrestrictions consists of RAT restriction, Forbidden Area, Service AreaRestrictions and Core Network type restriction, wherein the Core Networktype restriction defines whether UE is not allowed to connect to a corenetwork. For example, the Core Network type restriction parameter in a5GS network may have e.g. two values: one value may be “5GC”, indicatingthe UE is not allowed to connect to the core network of a 5GS network,the other value may be “EPC”, indicating the UE is not allowed toconnect to the core network of a EPS network. The Core Network typerestriction parameter of a UE may be found in subscription data of theUE. If subscription data of the UE does not include a Core Network typerestriction parameter, then the UE may be allowed to connect to e.g.both the core network of a 5GS network and the core network of an EPSnetwork.

SUMMARY

The abovementioned network capability and/or network restriction of a UEmay cause the UE in a first network will not connect to a secondnetwork, although the two networks are interworking with each other.This fact may cause a problem for a PDU session procedure for the UE.

The inventors of the present disclosure find, in the current mechanismsfor a PDU session procedure for a UE in a first communication networkinterworking with a second communication network, the following problemexists: if a node supporting the interworking is selected to manage thePDU session, the node will blindly allocate resources for the PDUsession regardless of whether the PDU session supports interworking withthe second network. For example, the node supporting the interworkingand selected for managing the PDU session will allocate resources forthe PDU session in the second communication network, in despite of thePDU session not supporting interworking with the second network, e.g.,due to lack of capability to connect to the second communication networkand/or due to restriction to connect to the second communicationnetwork.

The above problem occurs when a node supporting the interworking isselected for managing the PDU session which does not supportinterworking with the second network. As an example, for a 5GS network,the interworking with EPS is specified in Rel-15 and the SMF should havethe PGW-C capability from the very beginning. It's very likely that allthe SMFs deployed in the network have the PGW-C capability, i.e., allthe deployed SMFs are PGW-C+SMFs. In this case, no standalone SMF can beselected to manage a PDU session. Even if there are both standalone SMFsand combined PGW-C+SMFs in the deployment, a Network Repository Function(NRF), which may help the AMF to select a SMF to manage a PDU session,may make the selection without considering whether the PDU sessionsupports interworking with the second network, because the NRF doesn'tdifferentiate a standalone SMF and a combined PGW-C+SMF due to somereason (e.g., due to simple configuration of the NRF). In this case, aPGW-C+SMF may be selected to manage a PDU session.

One of the objects of the present disclosure is to resolve or alleviatethe above problem.

According to a first aspect of the present disclosure, the object isachieved by a method at a first node for facilitating a PDU sessionprocedure for a UE in a first communication network, wherein the firstcommunication network is interworking with a second communicationnetwork, and a second node supporting the interworking is selected formanaging the PDU session, the method comprising: determining anindication which indicates whether the PDU session supports interworkingwith the second communication network; and sending the indication to thesecond node.

According to a second aspect of the present disclosure, the object isachieved by a first node for facilitating a PDU session procedure for aUE in a first communication network, wherein the first communicationnetwork is interworking with a second communication network, and asecond node supporting the interworking is selected for managing the PDUsession, the first node comprising: determining unit, determining anindication which indicates whether the PDU session supports interworkingwith the second communication network; and sending unit, sending theindication to the second node.

According to a third aspect of the present disclosure, the object isachieved by a first node for facilitating a PDU session procedure for aUE in a first communication network, wherein the first communicationnetwork is interworking with a second communication network, and asecond node supporting the interworking is selected for managing the PDUsession, the first node comprising: a processor; and a memory, havingstored instructions that when executed by the processor cause the firstnode to determine an indication which indicates whether the PDU sessionsupports interworking with the second communication network, and sendthe indication to the second node.

According to a fourth aspect of the present disclosure, the object isachieved by a machine readable medium having stored thereon instructionsthat when executed on a first node cause the first node to perform themethod according to the first aspect.

According to a fifth aspect of the present disclosure, the object isachieved by a method at a second node for facilitating a PDU sessionprocedure for a UE in a first communication network, wherein the firstcommunication network is interworking with a second communicationnetwork, and the second node is supporting the interworking and isselected for managing the PDU session, the method comprising: receivingan indication indicating whether the PDU session supports interworkingwith second communication network from a first node; and determiningwhether the PDU session supports interworking with the secondcommunication network according to the indication.

According to a sixth aspect of the present disclosure, the object isachieved by a second node for facilitating a PDU session procedure for aUE in a first communication network, wherein the first communicationnetwork is interworking with a second communication network, and thesecond node is supporting the interworking and is selected for managingthe PDU session, the second node comprising: receiving unit, receivingan indication indicating whether the PDU session supports interworkingwith second communication network from a first node; and determiningunit, determining whether the PDU session supports interworking with thesecond communication network according to the indication.

According to a seventh aspect of the present disclosure, the object isachieved by a second node for facilitating a PDU session procedure for aUE in a first communication network, wherein the first communicationnetwork is interworking with a second communication network, and thesecond node is supporting the interworking and is selected for managingthe PDU session, the second node comprising: a processor; and a memory,having stored instructions that when executed by the processor cause thesecond node to receive an indication indicating whether the PDU sessionsupports interworking with second communication network from a firstnode; and determine whether the PDU session supports interworking withthe second communication network according to the indication.

According to an eighth aspect of the present disclosure, the object isachieved by a machine readable medium having stored thereon instructionsthat when executed on a second node cause the second node to perform themethod according to the fifth aspect.

The solutions of the present disclosure have at least one of thefollowing advantages:

-   -   improving allocation of resources for the PDU session procedure        for a UE in a communication network interworking with another        communication network, by considering whether the PDU session        supports interworking with second communication network;    -   increasing the resource utilization efficiency by means of        avoiding allocation of resources which are unnecessary for the        PDU session according to the indication and avoiding sending        them over NAS;    -   keeping the configuration in the NRF simple as well as        simplifying the deployment.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and benefits of the presentdisclosure will become more fully apparent from the following detaileddescription with reference to the accompanying drawings, in which likereference numerals or letters are used to designate like or equivalentelements. The drawings are illustrated for facilitating betterunderstanding of the embodiments of the disclosure and not necessarilydrawn to scale, in which:

FIG. 1 illustrates the non-roaming architecture for interworking between5GS and EPC/E-UTRAN;

FIG. 2 illustrates flowchart of the method at a first node according tothe present disclosure;

FIG. 3 illustrates flowchart of the method at a second node according tothe present dis closure;

FIG. 4 illustrates a UE requested PDU Session Establishment fornon-roaming and roaming with local breakout cases.

FIG. 5 is a schematic block diagram of a first node according to thepresent disclosure.

FIG. 6 is a schematic block diagram of a second node according to thepresent disclosure.

FIG. 7 is another schematic block diagram of a first node according tothe present disclosure.

FIG. 8 is another schematic block diagram of a second node according tothe present disclosure.

DETAILED DESCRIPTION

Embodiments herein will be described more fully hereinafter withreference to the accompanying drawings. The embodiments herein may,however, be embodied in many different forms and should not be construedas limiting the scope of the appended claims.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” “comprising,”“includes” and/or “including” when used herein, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

Also, use of ordinal terms such as “first,” “second,” “third,” etc.,herein to modify an element does not by itself connote any priority,precedence, or order of one element over another or the temporal orderin which acts of a method are performed, but are used merely as labelsto distinguish one element having a certain name from another elementhaving a same name (but for use of the ordinal term) to distinguish theelements.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

A flowchart of a method 200 at a first node for facilitating a PDUsession procedure for a UE in a first communication network is shown inFIG. 2, wherein the first communication network is interworking with asecond communication network, and a second node supporting theinterworking is selected for managing the PDU session, the methodcomprising the following steps: step 201 of determining an indicationwhich indicates whether the PDU session supports interworking with thesecond communication network; and step 202 of sending the indication tothe second node.

A flowchart of a method 300 at a second node for facilitating a PDUsession procedure for a UE in a first communication network is shown inFIG. 3, wherein the first communication network is interworking with asecond communication network, and the second node is supporting theinterworking and is selected for managing the PDU session, the methodcomprising: step 301 of receiving an indication indicating whether thePDU session supports interworking with second communication network froma first node; and step 302 of determining whether the PDU sessionsupports interworking with the second communication network according tothe indication.

Both the first node and the second node can be implemented as a networkelement on a dedicated hardware, as a software instance or a firmwarerunning on a hardware, as a virtualized function instantiated on anappropriate platform (e.g. on a cloud infrastructure), or as anycombination thereof.

Now, further embodiments will be described in connection with an exampleUE requested PDU session establishment in a 5GS network which isinterworking with an EPS network. It can be understood that, althoughthe further embodiments herein are described in the context of the 5GSand EPS networks, the embodiments can be also applied to other PDUsession procedures in other different telecommunication networksinterworking with each other, if the same problem exists in theirmechanisms for the PDU session procedures. It will be also understoodthat, although specific terms are used in the embodiments, theembodiments are not limited to those specific terms but may be appliedto all similar entities. For example, the “user equipment”/“UE” hereinmay refer to e.g. user terminal, station, terminal, terminal node, andso on.

A UE requested PDU session establishment is a common PDU sessionprocedure for a UE. The procedure is used to establish a new PDUSession, handover a PDN Connection in EPS to PDU Session in 5GS withoutN26 interface, switch an existing PDU Session between non-3GPP accessand 3GPP access, or request a PDU Session for Emergency services.

FIG. 4 illustrates a UE requested PDU Session Establishment fornon-roaming and roaming with local breakout cases. At step 1 in FIG. 4,the UE initiates the UE Requested PDU Session Establishment procedure bythe transmission of a NAS message containing a PDU Session EstablishmentRequest. The PDU Session Establishment Request includes necessaryinformation such as a PDU session ID, Requested Type, a Requested SSCmode, and so on. At step 2 in FIG. 4, the AMF may utilize the NRF todiscover the SMF instance(s) unless SMF information is available byother means, e.g. locally configured on AMF. The NRF provides the IPaddress or the FQDN (Fully Qualified Domain Name) of SMF instance(s) orEndpoint Address(es) of SMF service instance(s) to the AMF. The SMFselection function in the AMF selects an SMF instance based on theavailable SMF instances obtained from NRF or on the configured SMFinformation in the AMF. At step 3 in FIG. 4, the AMF sends to the SMFeither a Nsmf_PDUSession_CreateSMContext Request or aNsmf_PDUSession_UpdateSMContext Request. If the AMF does not have anassociation with an SMF for the PDU Session ID provided by the UE (e.g.when Request Type indicates “initial request”), the AMF invokes theNsmf_PDUSession_CreateSMContext Request, but if the AMF already has anassociation with the SMF for the PDU Session ID provided by the UE (e.g.when Request Type indicates “existing PDU Session”), the AMF invokes theNsmf_PDUSession_UpdateSMContext Request. After step 9 and before step 12in FIG. 4, if the selected SMF is a PGW-C+SMF and the PGW-C+SMFdetermines that EPS bearer ID(s) needs to be assigned to the QoS flow(s)in the PDU Session, the PGW-C+SMF invokes aNamf_Communication_EBIAssignment Request including PDU Session ID andARP list to the AMF (not illustrated in FIG. 4). The ARP list indicatesthe number of the requested EBIs, and the corresponding ARP. The AMFuses the ARP list (including ARP priority level, the pre-emptioncapability and the pre-emption vulnerability) and the Single NetworkSlice Selection Assistance Information (S-NSSAI) to prioritize the EBIrequest, the AMF can revoke the EBI from an ongoing lower priority PDUSession, if the maximum number of EBIs have been reached and a sessionwith a higher priority requests an EBI. The AMF responds the PGW-C+SMFwith a cause which indicates whether the assignment is successful or notin a Namf_Communication_EBIAssignment response. If the assignment issuccessful, the AMF provides a list of <ARP, EBI> pair to the consumerNF. Steps similar to the abovementioned steps also occur in aUE-requested PDU Session Establishment for home-routed roaming scenarios(not illustrated).

The AMF and the selected PGW-C+SMF in the above procedure can act as thefirst node and the second node of the present disclosure respectively.The AMF can determine an indication which indicates whether the PDUsession supports interworking with the EPS network, which may meanwhether the allocation of resources for the PDU session is needed, e.g.,indicates whether the PDU session can be moved to the EPS network, andsend the indication to the PGW-C+SMF to let it allocate the resources ornot. Particularly, if determining the PDU session does not supportinterworking with the EPC network, the AMF determines no resources ofthe EPS network for the PDU session (e.g., the resources are resourcesfor a bearer in the EPC network in an embodiment) should be allocated;otherwise, the AMF determines resources of the EPS network for the PDUsession may be allocated. Then, the AMF may send the indication to thePGW-C+SMF. The PGW-C+SMF may determine whether the PDU session supportsinterworking with the EPS network according to the indication, e.g., inorder to allocate resources for the PDU session accordingly.

In an embodiment, when determining the PDU session does not supportinterworking with the second network, the AMF may send to the PGW-C+SMFthe indication indicating that the PDU session does not supportinterworking with the EPS network, e.g., inNsmf_PDUSession_CreateSMContext Request. When the PGW-C+SMF receivessuch an indication, the PGW-C+SMF should skip preparation for allocatingthe resources for the PDU session in the EPC network to avoid waste ofthe resources and improve efficiency of the allocation. However, if thePGW-C+SMF has not been upgraded to realize the indication, the PGW-C+SMFhaving received the indication may still send a request related toallocating the resources to the AMF, e.g., aNamf_Communication_EBIAssignment Request to request the AMF to allocatean ID of a bearer in the EPS network. In this case, the AMF can rejectthe request from the PGW-C+SMF, e.g., by returning a new failure cause(“EPS interworking not supported” or something similar) in a response,e.g., in the Namf_Communication_EBIAssignment response. Then, thePGW-C+SMF will skip the preparation work for allocation of theresources, e.g. mapping to EPS bearer is not performed. In anotherembodiment, the AMF may just reject the request from the PGW-C+SMF,without beforehand sending to the PGW-C+SMF an indication that the UEwill not connect to the EPC network.

In an embodiment, when determining the PDU session supports interworkingwith the second network, the AMF may send to the PGW-C+SMF theindication indicating that the PDU session supports interworking withthe EPS network, e.g., in Nsmf_PDUSession_CreateSMContext Request. In anembodiment, when the PDU session supports interworking with the EPSnetwork, the indication from the AMF further indicates whether a N26interface between the 5GS network and the EPS network is to be used forthe interworking of the PDU session. When the PGW-C+SMF receives such anindication, the PGW-C+SMF may allocate the resources for the PDU sessionin the EPC network. For example, the PGW-C+SMF may send a request toallocate resources for the PDU session in the EPS network to the AMF. Inan embodiment, the PGW-C+SMF may send a request to allocate an identityof a bearer in the EPS network for the PDU session to the AMF, when theindication indicates the N26 interface is to be used for theinterworking of the PDU session. In another embodiment, the PGW-C+SMFmay store information of the PDU session in a third node (e.g., in aUnified Data Management, UDM) without sending a request to allocate anidentity of a bearer in the EPS network for the PDU session to the AMF,when the indication indicates the N26 interface is not to be used forthe interworking of the PDU session. In an embodiment, when the N26interface is not to be used for the interworking of the PDU session, ifthe AMF receives a request to allocate an identity of a bearer in theEPS network for the PDU session from the PGW-C+SMF, the AMF should senda response to reject the request to the PGW-C+SMF.

The indication can be determined by the AMF in various ways, e.g., theAMF determines the indication by itself or by obtaining information fromanother node. In an embodiment, whether the PDU session supportsinterworking with the EPS network or not is determined based on the UE'scapability and/or a subscription data of the UE, which may indicate arestriction to connect to the EPS network. In an embodiment, whether thePDU session supports interworking with the EPS network or not mayfurther be determined based on network configuration. In an embodiment,the UE's capability may include the network capability information ofthe UE, e.g., the MM Core Network Capability information of the UE. Inan embodiment, the subscription data of the UE may include, e.g., theCore Network type restriction parameter of a UE. For example, if theUE's MM Core Network Capability IE indicates “S1 mode supported” and thevalue of the Core Network type restriction parameter of the UE is not“EPC” (or the Core Network type restriction parameter does not exist atall), it can be determined that the PDU session supports interworkingwith the EPS network; otherwise, the PDU session does not supportinterworking with the EPS network.

FIG. 5 illustrates a schematic block diagram of a first node 500according to the present disclosure. The first node 500 (e.g., an AMF)may facilitate a PDU session procedure for a UE in a first communicationnetwork (e.g., a 5GS network), wherein the first communication networkis interworking with a second communication network (e.g., an EPSnetwork), and a second node (e.g., a PGW-C+SMF) supporting theinterworking is selected for managing the PDU session. The first node500 may include a determining unit 501, for determining the PDU sessionsupports interworking with the second network; and a sending unit 502,for sending the indication to the second node.

FIG. 6 illustrates a schematic block diagram of a second node 600according to the present disclosure. The second node 600 (e.g., aPGW-C+SMF) may facilitate a PDU session procedure for a UE in a firstcommunication network (e.g., a 5GS network), wherein the firstcommunication network is interworking with a second communicationnetwork (e.g., an EPS network), and the second node is supporting theinterworking and is selected for managing the PDU session. The secondnode 600 may include a receiving unit 601, for receiving an indicationindicating whether the PDU session supports interworking with secondnetwork from a first node; and a determining unit 602, for determiningwhether the PDU session supports interworking with the second networkaccording to the indication.

It can be appreciated that, the first node 500 and the second node 600described herein may be implemented by various units, so that each ofthe first node 500 and the second node 600 implementing one or morefunctions described with the embodiments may comprise not only theunit(s) shown in the corresponding figure, but also other units forimplementing one or more functions thereof. In addition, each of thefirst node 500 and the second node 600 may comprise a single unitconfigured to perform two or more functions, or separate units for eachseparate function. Moreover, the units may be implemented in hardware,firmware, software, or any combination thereof.

It is understood that blocks of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, may be implemented by computer programinstructions. These computer program instructions may be provided to aprocessor of a general purpose computer, special purpose computer,and/or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer and/or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the blockdiagrams and/or flowchart block or blocks.

Furthermore, the solution of the present disclosure may take the form ofa computer program on a memory having computer-usable orcomputer-readable program code embodied in the medium for use by or inconnection with an instruction execution system. In the context of thisdocument, a memory may be any medium that may contain, store, or isadapted to communicate the program for use by or in connection with theinstruction execution system, apparatus, or device.

Therefore, the present disclosure also provides a first node 700including a processor 701 and a memory 702, as shown in FIG. 7. In thefirst node 700, the memory 702 stores instructions that when executed bythe processor 701 cause the first node 700 to perform the method at thefirst node described above with the embodiments. The present disclosurealso provides a second node 800 including a processor 801 and a memory802, as shown in FIG. 8. In the second node 800, the memory 802 storesinstructions that when executed by the processor 801 cause the secondnode 800 to perform the method at the second node described above withthe embodiments.

The present disclosure also provides a machine readable medium (notillustrated) having stored thereon instructions that when executed on afirst node cause the first node to perform the method at the first nodedescribed with the above embodiments. The present disclosure alsoprovides a machine readable medium (not illustrated) having storedthereon instructions that when executed on a second node cause thesecond node to perform the method at the second node described with theabove embodiments.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyimplementation or of what may be claimed, but rather as descriptions offeatures that may be specific to particular embodiments of particularimplementations. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or variation of a sub-combination.

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The above described embodiments are given for describing ratherthan limiting the disclosure, and it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit and scope of the disclosure as those skilled in the artreadily understand. Such modifications and variations are considered tobe within the scope of the disclosure and the appended claims. Theprotection scope of the disclosure is defined by the accompanyingclaims.

1. A method at a first node for facilitating a Protocol Data Unit (PDU)session procedure for a User Equipment (UE) in a first communicationnetwork, wherein the first communication network is interworking with asecond communication network, and a second node supporting theinterworking is selected for managing the PDU session, the methodcomprising: determining an indication which indicates whether the PDUsession supports interworking with the second network; and sending theindication to the second node.
 2. The method of claim 1, wherein whetherthe PDU session supports interworking with the second network compriseswhether the PDU session can be moved to the second network.
 3. Themethod of claim 1, wherein the determining is based on networkconfiguration.
 4. The method of claim 1, wherein the determining isfurther based on UE's capability, a subscription data of the UE, or boththe UE's capability and the subscription data of the UE.
 5. The methodof claim 4, wherein the UE's capability comprises Core NetworkCapability information of the UE, and the subscription data of the UEcomprises core network type restriction to the second communicationnetwork.
 6. The method of claim 4, wherein a value of UE's capabilitycomprises S1 mode supported or N1 mode supported.
 7. The method of claim4, wherein a value of the subscription data of the UE comprises EPC orSGC, or the value does not exist.
 8. The method of claim 1, wherein thePDU session procedure is a PDU session establishment.
 9. The method ofclaim 1, further comprising: receiving a request to allocate resourcesfor the PDU session in the second network from the second node.
 10. Themethod of claim 9, further comprising: sending a response to reject therequest to allocate resources for the PDU session in the second networkto the second node, when the indication indicates the PDU session notsupporting interworking with the second network.
 11. The method of claim9, wherein the first communication network is a 5th Generation System(5GS) network, the second communication network is an Evolved PacketSystem (EPS) network, the first node is an Access and MobilityManagement Function (AMF), and the second node is a Packet Data NetworkGateway Control plane Function+Session Management Function (PGW-C+SMF).12. The method of claim 11, wherein the resources comprise EPS beareridentity.
 13. The method of claim 11, wherein when the PDU sessionsupports interworking with the second network, the indication furtherindicates whether a N26 interface between the 5GS network and the EPSnetwork is to be used for the interworking of the PDU session.
 14. Themethod of claim 13, further comprising sending a response to reject arequest to allocate an identity of a bearer in the EPS network for thePDU session from the PGW-C+SMF, when the N26 interface is not to be usedfor the interworking of the PDU session.
 15. A first node forfacilitating a PDU session procedure for a UE in a first communicationnetwork, wherein the first communication network is interworking with asecond communication network, and a second node supporting theinterworking is selected for managing the PDU session, the first nodecomprising: a processor; and a memory, having stored instructions that,when executed by the processor, cause the first node to: determine anindication which indicates whether the PDU session supports interworkingwith the second network; and send the indication to the second node.16-17. (canceled)
 18. A method at a second node for facilitating a PDUsession procedure for a UE in a first communication network, wherein thefirst communication network is interworking with a second communicationnetwork, and the second node is supporting the interworking and isselected for managing the PDU session, the method comprising: receivingan indication indicating whether the PDU session supports interworkingwith second network from a first node; and determining whether the PDUsession supports interworking with the second network according to theindication.
 19. The method of claim 18, wherein whether the PDU sessionsupports interworking with the second network comprises whether the PDUsession can be moved to the second network.
 20. The method of claim 18,wherein the PDU session procedure is a PDU session establishment. 21.The method of claim 18, further comprising: sending a request toallocate resources for the PDU session in the second network to thefirst node.
 22. The method of claim 21, further comprising: receiving aresponse to reject the request to allocate resources for the PDU sessionin the second network from the first node, when the indication indicatesthe PDU session not supporting interworking with the second network. 23.The method of claim 21, further comprising: skipping preparation forallocating resources for the PDU session in the second network, whendetermining that the PDU session does not support interworking with thesecond network.
 24. The method of claim 21, the first communicationnetwork is a 5th Generation System (5GS) network, the secondcommunication network is an Evolved Packet System (EPS) network, thefirst node is an Access and Mobility Management Function (AMF), and thesecond node is a Packet Data Network Gateway Control planeFunction+Session Management Function (PGW-C+SMF).
 25. The method ofclaim 24, wherein the resources comprise EPS bearer identity. 26.(canceled)
 27. The method of claim 24, further comprising: sending arequest to allocate an identity of a bearer in the EPS network for thePDU session to the AMF, when the indication indicates a N26 interfacebetween the 5GS network and the EPS network is to be used for theinterworking of the PDU session.
 28. The method of claim 24, furthercomprising: storing information of the PDU session in a third node, whenthe indication indicates a N26 interface between the 5GS network and theEPS network is not to be used for the interworking of the PDU session.29. A second node for facilitating a PDU session procedure for a UE in afirst communication network, wherein the first communication network isinterworking with a second communication network, and the second node issupporting the interworking and is selected for managing the PDUsession, the second node comprising: a processor; and a memory, havingstored instructions that, when executed by the processor, cause thesecond node to: receive an indication indicating whether the PDU sessionsupports interworking with the second network from a first node; anddetermine whether the PDU session supports interworking with the secondnetwork according to the indication. 30-31. (canceled)